A wood truss consists of multiple planks of lumber joined together via metal connector plates, commonly referred to as truss plates. A wood truss typically comprises top and bottom chords joined by web members to form various triangular patterns. The design of a wood truss involves selecting a span and pitch to satisfy a particular architectural plan and then utilizing various engineering methods to determine the shape of the truss and the web pattern required, as well as the size and length of each member required based upon the various loads that the truss may be subjected to during use.
Because of the size of a typical truss (e.g., one that is 45 feet in length), truss fabrication is typically performed on one or a series of fabrication tables. The lumber planks are placed on the fabrication tables in an arrangement to match the final desired shape of the truss. Truss plates having impaling members extending from one side are placed at each joint where the ends of the lumber planks are to be joined. Typically, a system of pressure rollers is used to embed the impaling members of each truss plate into the lumber planks to create a truss.
To achieve a strong connection at each joint, it is necessary that the impaling members of each truss plate are pressed firmly into the wood. This is accomplished by pressing each truss plate downwardly against the surface of the truss table, which provides the resistance necessary to ensure the firm embedment of each truss plate. Unfortunately, when a series of spaced-apart truss tables are employed, the size and configuration of a wood truss often results in one or more truss joints being unsupported by a truss table. As a result, pedestals are typically positioned under these truss plates to provide resistance during the pressing operation. Of course, the pedestals provide less support, and the use of pedestals between truss tables hampers the movement of operators who move therebetween to place lumber planks and truss plates on the truss tables. Consequently, the use of pedestals is discouraged.
Many truss tables utilize an ejector unit for raising a truss so that it may be removed easily from the truss table when completed. An ejector unit typically resides within and extends from a slot in the surface of each truss table. It is desirable to avoid locating a truss joint directly over an ejector unit slot because of the risk of inadequate resistance during pressing of a truss plate into the joint area.
A particularly time-consuming task associated with truss fabrication is the process of setting up the truss tables for a particular truss configuration. A set-up system typically includes placing a number of jigging fixtures and/or mechanical stops on each truss table in a pattern matching that of the truss configuration. Typically, the mechanical stops are used to hold the top and bottom chords in place. The remaining planks for each truss are precut to the proper length and end angle and are arranged on the fabrication tables in the correct triangulated truss configuration prior to being fixed into that configuration with truss plates.
Each mechanical stop typically includes some means for being secured to a fabrication table. Often times a graduated scale is attached to each table adjacent each slot. Once positioned, the mechanical stops are tightened down so as to provide a solid location against which the truss planks may be held in place. The positions of the mechanical stops may be determined in advance for a truss either manually or by a software program associated with the set-up system, such as the FREEFORM.TM. program offered by Tee-Lok Corporation, Edenton, N.C. Once the planks are arranged on the truss tables, they are attached to one another by a pressure roller, such as that described above, which presses a truss plate into each joint area to form the truss. The completed truss is removed from the table via the ejector unit, and another set of planks is guided into position within the mechanical stops. The mechanical stops remain in place until all trusses of the selected configuration have been formed. They are then re-positioned on the truss tables to define the next truss configuration to be fabricated.
Unfortunately, the process of positioning and repositioning the mechanical stops has the tendency to slow truss production considerably. This is particularly true when sets of trusses of significantly different configuration are constructed sequentially, as this requires considerable repositioning of the cogs.
Trusses are often transported via an expandable rollerbed trailer. Trusses are often large and irregularly shaped, making the task of fitting a load of trusses onto an expandable rollerbed trailer a somewhat difficult and costly task. Adding to the cost of truss transportation are shipping regulations which often limit the "over-length" and "over-width" dimensions of materials transported on expandable rollerbed trailers. If truss overhang exceeds that permitted by law, special permits are often required. These special permits often limit the routes and times of travel, thus adding to the cost of truss transportation. In addition, it is often desirable to load an expandable rollerbed trailer in such a way that the trusses can be unloaded at a construction site in the order in which they will be used during construction. Each of these factors can render the loading of trusses onto an expandable rollerbed trailer an expensive and time consuming trial and error operation.